CN103227262A - LED reflector crystal containing left-handed material and preparation method - Google Patents
LED reflector crystal containing left-handed material and preparation method Download PDFInfo
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Abstract
The invention discloses an LED (light emitting diode) reflector crystal containing a left-handed material and a preparation method. The LED reflector crystal has structural characteristics as follows: (1), a current diffusing layer is arranged at the bottom of a reflector; (2), the reflector is structurally formed by arraying a right-handed material and the left-handed material alternately; (3), gaps in a left-handed material layer are in fishing net structures, and are filled with solid gain materials to reduce losses and improve the performance of the left-handed material; and (4), a substrate of the reflector is made of conducting metal. In the aspect of preparation technologies, the higher-accuracy technologies such as electron beam etching, electron beam evaporation and dry etching (ICP (inductively coupled plasma) and RIE (reactive ion etching)) are combined to prepare the LED reflector to improve the performance of the reflector, and the LED reflector crystal is in a photonic crystal structure piled by the left-handed material and the right-handed material alternately, so that the light-intensity losses can be reduced, the reflection efficiency can be improved, and the luminous efficiency of an LED is improved.
Description
Technical field
The invention belongs to the opto-electronic device technology of preparing, particularly a kind of LED extension chip structure and preparation method as reflective mirror.
Background technology
Semiconductor light-emitting-diode (Light Emitting Diode, LED) application is extremely widely arranged in signal demonstration, backlight and solid-state illumination field, especially use morely based on the LED of III-V compounds of group gallium nitride (GaN) material, have characteristics such as high brightness, low energy consumption, long-life, response speed be fast.Vertical stratification LED(Vertical Light Emitting Diode VLED) with respect to horizontal structure LED, has perfect heat-dissipating, the luminous efficiency height, and therefore advantages such as life-span length are the important developing direction of LED.
Since the notion of John and Yabolonivitch1987 proposition photonic crystal, photonic crystal not only becomes the important research field of micro-nano optoelectronics and quantum optices, and is used widely in Information Optics and other a plurality of subjects.The typical feature of photonic crystal is to have photon band gap, can effectively control frequency and direction that photon (electromagnetic wave) is propagated, and have low-loss advantage.
1967, the physicist Veselago of the former Soviet Union has proposed a kind of left-handed materials (Left-handed material, abbreviation LHM) notion, the DIELECTRIC CONSTANT of this material and magnetic permeability μ are negative value, constitute the left hand relation between electric field, magnetic field and the wave vector, refractive index is a negative value, so be also referred to as material with negative refractive index (negative index of refraction material is called for short NIM).Calendar year 2001, the physicists such as David Smith in California, USA university San Diego branch school utilize the left-handed materials that produces microwave band based on the composite material of copper first, and left-handed materials has attracted increasing concern afterwards, and development is swift and violent.2003 and 2006, twice competition of U.S.'s " science " magazine left-handed materials was one of annual global ten big sciences progress.Left-handed materials can be at microwave device as a kind of special material, field performance enormous function such as perfect lens, military stealthy and information communication.
There is the shortcoming of narrow bandwidth by the photonic crystal of right-handed material preparation, limited the performance and the application of photonic crystal.(the Wang ZY of Zhejiang University, Chen XM, et al.Photonic crystal narrow filters withnegative refractive index structuraldefects.Progress in Electromagnetics Research, PIER, 2008,80,421) it is more much bigger than traditional photonic crystal to propose to contain the band gap of photonic crystal of left-handed materials, and has narrow transmission band.(the Shumin Xiao of U.S. Purdue university, Vladimir P.Drachev, et al.Loss-free and active optical negative-indexmetamaterials.Nature.2010,466,735) propose leftward to add in the material gain material and help reducing intensity loss, strengthen resonance effect, improve the performance of left-handed materials.Gunnar Dolling (Gunnar Dolling, Christian Enkrich.Simultaneous Negative Phaseand Group Velocity of Lightin a Metamaterial.Science.2006,312,892) the fishing net type structure of proposition nanometer scale can produce the characteristic of left-handed materials, can replace traditional metal openings resonant ring array (SRRs) structure, simplify technological process.
What above document related to is to left-handed materials and by the photonic crystal The Characteristic Study that right-hand man's material constitutes, and does not relate to its application in LED.That relate in the patent in the past is the preparation technology of left-handed materials, does not relate to the design and the preparation of the photon crystal structure that contains right-hand man's material, does not also relate to the application in LED.
Summary of the invention
The objective of the invention is to, a kind of LED reflective mirror crystal structure and preparation technology who contains left-handed materials is provided,, improve reflection efficiency, thereby improve the luminous efficiency of LED to reduce intensity loss.
For reaching above purpose, the present invention takes following technical scheme to be achieved:
A kind of LED reflective mirror crystal that contains left-handed materials: comprise the n-GaN layer from top to bottom successively, multiple quantum well active layer, the p-GaN layer, it is characterized in that, one current-diffusion layer is set below the p-GaN layer, be provided with below this current-diffusion layer and be no less than three layers conductive metal layer, below last one deck conductive metal layer a bonding metal layer is set, wherein, each conductive metal layer faying face is provided with the array that rectangular cavity is arranged, fill the solid state gain material in all rectangular cavity, form left-handed materials zone A, the plane domain that does not have the rectangular cavity array in the same conductive metal layer is the right-handed material area B, and left-handed materials zone A and right-handed material area B alternately fold; Described each rectangular cavity girth is 120～600nm; The unit distance L of array
1, L
2Be no more than 250nm.
In the such scheme, the girth of described rectangular cavity is 160～320nm; The unit distance L of array
1=L
2, all get 120nm～180nm.Described current-diffusion layer is made by ITO or Graphene.Described conductive metal layer is made by Ag, Al, Au or Cu.Described bonding metal layer is made by Cu or Cu/W alloy.Described solid state gain material is an epoxy resin.
The aforementioned preparation method who contains the LED reflective mirror crystal of left-handed materials is characterized in that: comprise the steps:
(1) the p-GaN laminar surface at LED extension chip deposits the current-diffusion layer of a layer thickness at 10～20nm;
(2) on current-diffusion layer, deposit the conductive metal layer of a layer thickness at 20～60nm;
(3) be that 15～25nm, girth are the rectangular cavity array of 120～600nm at conductive metal layer upper surface etching depth, the unit distance L of array
1, L
2Be no more than 250nm;
(4) at conductive metal layer surface deposition one deck solid state gain material, fill up the rectangular cavity array of etching;
(5) adopt the method for dry etching with the equating of conducting metal laminar surface;
(6) repeating step (2)～(5) is at least 3 times, makes the gross thickness of conductive metal layer be no more than 300nm;
(7) in the end the enterprising line unit of one deck conductive metal layer closes, and at last the Sapphire Substrate of LED extension chip is peeled off.
In the said method, the deposition of current-diffusion layer adopts the mode of thermal evaporation in the described step (1).The deposition of conductive metal layer adopts the electron beam evaporation plating mode in the described step (2), and conducting metal is Al, Ag, Au or Cu.Rectangular cavity array etching adopts the electron beam lithography mode in the described step (3).
LED reflective mirror crystal preparation technology's the advantage that the present invention contains left-handed materials is as follows:
1, adopts the mode of dry etching and electron beam evaporation plating,, have higher precision with respect to other preparation technology.Up to the present, the precision of electron beam lithography can be controlled within the 10nm, and electron beam deposition technology can be controlled in the 1nm scope.The raising of preparation precision helps analyzing, controlling and improve the performance of LED reflective mirror;
2, at p-GaN surface preparation reflective mirror, can not destroy the epitaxial structure of led chip, guaranteed the quality of led chip.
3, metal level is divided into repeatedly deposition, is convenient to the structure and the performance of left-handed materials.
Adopt the structural advantages of the LED reflective mirror crystal of the inventive method preparation to be:
1, the bottom is one deck current-diffusion layer, can prevent that electric current from blocking up, and technical maturity.
2, the substrate material of reflective mirror is conducting metal (Al, Ag, Au, Cu), has reduced the influence to the electric property of LED, and is convenient to the preparation of left-handed materials.
3, this reflective mirror crystal structure is that one deck right-handed material and one deck left-handed materials are alternately arranged, and its photon band gap is wideer than traditional photonic crystal, and the reflection of light rate is obviously improved.
4, the left-handed materials zone is the fishing net structure, and fills the solid state gain material, can reduce loss, strengthens the performance of left-handed materials.
Description of drawings
The present invention is described in further detail below in conjunction with the drawings and specific embodiments.
Fig. 1 is the LED reflective mirror crystal structure schematic diagram that the present invention contains left-handed materials.
Fig. 2 is the top plan view on A surface, Fig. 1 left-handed materials zone.
Fig. 3 is preparation technology's flow chart of Fig. 1 structure.
Fig. 4 is the epitaxial crystal configuration state variation diagram by preparation technology of the present invention.Wherein: a figure is the extension chip of original LED; B figure is the structure of deposition one deck ITO; C figure is the structure behind deposition one deck Ag; D figure is the structure behind the electron beam lithography; E figure is the structure after gain material is filled; F figure is the structure after the left-handed materials surface equating; G figure is the structure of deposit multilayer right-hand man material; H figure is the structure behind the bonding; I figure is the structure after chip is inverted; J figure is the structure behind the laser lift-off.
Fig. 5 is Re provided by the invention (n) curve and FOM curve.Among the figure: the real part of solid line (Re (n))-effective refractive index; Dotted line (FOM)-quality factor.
Fig. 6 is a transmission spectrum provided by the invention.
Fig. 7 is a LED optical output power curve provided by the invention.
Embodiment
Referring to Fig. 1, a kind of LED reflective mirror crystal structure that contains left-handed materials, comprise n-GaN layer 1 from top to bottom successively, multiple quantum well active layer (MQW active layer) 2, p-GaN layer 3, current-diffusion layer 4 (ITO or Graphene), three layers of conductive metal layer 5 (Ag, Al, Au or Cu), bonding metal layer 7 (Cu/W), wherein, each conductive metal layer faying face is provided with the array that rectangular cavity is arranged, fill solid state gain material 6 (epoxy resin) in all rectangular cavity, form left-handed materials zone A, this similar fishing net structure of this left-handed materials zone A can reduce loss, strengthens the performance of left-handed materials; The zone that does not have the rectangular cavity array in the same conductive metal layer is the right-handed material area B, and left-handed materials zone A and right-handed material area B alternately fold.
With reference to figure 2, the rectangular cavity length of side d in the left-handed materials zone
1=d
2, can between 30nm～150nm, select, present embodiment selects 40nm～80nm.The rectangular cavity pattern is array planar, and is covered with whole plane, the unit distance L of array
1=L
2, get 100nm～250nm, present embodiment selects 120nm～180nm.
Referring to Fig. 3, Fig. 4, the preparation method that the present invention contains the LED reflective mirror crystal of left-handed materials comprises:
Step 1: provide the extension chip of a LED, as Fig. 4 a.The LED that the present invention uses comprises horizontal structure, vertical stratification, quantum dot LED structure.
Step 2: as current-diffusion layer 4, can select in 10nm, 15nm, three data of 20nm, sees Fig. 4 b by thickness at the p-GaN of LED layer 3 surface deposition one deck ITO (Indium Tin Oxides) or Graphene for the mode that adopts thermal evaporation.
Step 3: mode (Electron beam evaporation) deposition one deck Ag(of employing electron beam evaporation plating or Al, Au, Cu) as conductive metal layer 5, thickness can be selected in 30nm, 40nm, four data of 50nm, 60nm, sees Fig. 4 c.
Step 4: the mode that adopts electron beam lithography is at Ag laminar surface etching rectangular cavity array pattern (Fig. 2), and etching depth is got 20nm, also desirable 15nm, 25nm.The length of side d1 of rectangular cavity array pattern, d2 all get 50nm, also can get 60nm, 70nm, 80nm, the unit distance L of array respectively
1, L
2All get 150nm, also desirable 120nm, 140nm, 160nm, 180nm see Fig. 4 d.
Step 5: adopt the mode of spin coating (Spin-coating process) to be coated with last layer solid state gain layer 6 at the Ag laminar surface, can adopt the epoxy resin that is mixed with rhodamine800 (Rh800), epoxy resin must fill up the rectangular cavity space of etching, sees Fig. 4 e.
Step 6: adopt the method for dry etching, adopt inductively coupled plasma etching (ICP) here, perhaps reactive ion etching (RIE) is seen Fig. 4 f with the equating of Ag laminar surface.
Step 7: repeating step 2～6 steps 3 time, see Fig. 4 g.Also desirable 4 times, 5 times, 6 times, but the gross thickness＜300nm of metal level.
Step 8: in the end the enterprising line unit of one deck Ag closes, and bonding material is the Cu/W alloy, and also desirable Cu, the thickness of bonding metal layer 7 are 100 μ m, also can be 120 μ m, and 140 μ m see Fig. 4 h.
Step 9: chip is inverted, is adopted the mode of laser lift-off (Laser liftoff) that Sapphire Substrate 8 (substrate) is peeled off then, see Fig. 4 i, Fig. 4 j.
Other technological processes and the condition that relate in this example are common process, belong to the category that this area is familiar with, and do not repeat them here.
It is exemplary more than describing the explanation that content of the present invention is carried out; it is not the formation limiting the scope of the invention; on the basis of technical scheme of the present invention, the those skilled in the art need not pay various modifications that creative work can make or distortion still within protection scope of the present invention.
Adopt the inventive method gained LED reflective mirror crystal after testing, to find, left-handed materials structure (regional A) can produce the negative index characteristic at visible light wave range, and its quality factor (Figure of Merit, FOM) higher, referring to Fig. 5, solid line is represented the real part of effective refractive index among the figure, and dotted line is represented FOM, FOM=-Re (n)/Im (n) wherein, the imaginary part of Im (n) expression effective refractive index.
Left-handed materials (regional A) constitutes special photonic crystal (effect shows as the LED reflective mirror) with right-handed material (area B) alternating deposit, its band gap is wideer than the band gap of traditional photonic crystal, the transmission band is narrower, and the intensity in transmission decay rapidly, the reflection of light effect is obviously improved, referring to Fig. 6.
This LED mirror construction is applied among the LED, can increase the light intensity of exiting surface, and reduce reflection loss effectively with injecting the light reflection of bottom, has improved the power output of LED.
Claims (10)
1. LED reflective mirror crystal that contains left-handed materials: comprise the n-GaN layer from top to bottom successively, multiple quantum well active layer, the p-GaN layer, it is characterized in that, one current-diffusion layer is set below the p-GaN layer, be provided with below this current-diffusion layer and be no less than three layers conductive metal layer, below last one deck conductive metal layer a bonding metal layer is set, wherein, each conductive metal layer faying face is provided with the array that rectangular cavity is arranged, fill the solid state gain material in all rectangular cavity, form left-handed materials zone A, the plane domain that does not have the rectangular cavity array in the same conductive metal layer is the right-handed material area B, and left-handed materials zone A and right-handed material area B alternately fold; Described each rectangular cavity girth is 120～600nm; The unit distance L of array
1, L
2Be no more than 250nm.
2. the LED reflective mirror crystal that contains left-handed materials as claimed in claim 1 is characterized in that the girth of described rectangular cavity is 160～320nm; The unit distance L of array
1=L
2, all get 120nm～180nm.
3. the LED reflective mirror crystal that contains left-handed materials as claimed in claim 1 is characterized in that described current-diffusion layer is made by ITO or Graphene.
4. the LED reflective mirror crystal that contains left-handed materials as claimed in claim 1 is characterized in that described conductive metal layer is made by Ag, Al, Au or Cu.
5. the LED reflective mirror crystal that contains left-handed materials as claimed in claim 1 is characterized in that described bonding metal layer is made by Cu or Cu/W alloy.
6. the LED reflective mirror crystal that contains left-handed materials as claimed in claim 1 is characterized in that described solid state gain material is an epoxy resin.
7. a preparation method who contains the LED reflective mirror crystal of left-handed materials is characterized in that: comprise the steps:
(1) the p-GaN laminar surface at LED extension chip deposits the current-diffusion layer of a layer thickness at 10～20nm;
(2) on current-diffusion layer, deposit the conductive metal layer of a layer thickness at 20～60nm;
(3) be that 15～25nm, girth are the rectangular cavity array of 120～600nm at conductive metal layer upper surface etching depth, the unit distance L of array
1, L
2Be no more than 250nm;
(4) at conductive metal layer surface deposition one deck solid state gain material, fill up the rectangular cavity array of etching;
(5) adopt the method for dry etching with the equating of conducting metal laminar surface;
(6) repeating step (2)～(5) is at least 3 times, makes the gross thickness of conductive metal layer be no more than 300nm;
(7) in the end the enterprising line unit of one deck conductive metal layer closes, and at last the Sapphire Substrate of LED extension chip is peeled off.
8. the preparation method who contains the LED reflective mirror crystal of left-handed materials as claimed in claim 7 is characterized in that: the deposition of current-diffusion layer adopts the mode of thermal evaporation in the described step (1).
9. the preparation method who contains the LED reflective mirror crystal of left-handed materials as claimed in claim 7 is characterized in that: the deposition of conductive metal layer adopts the electron beam evaporation plating mode in the described step (2), and conducting metal is Al, Ag, Au or Cu.
10. the preparation method who contains the LED reflective mirror crystal of left-handed materials as claimed in claim 7 is characterized in that: rectangular cavity array etching adopts the electron beam lithography mode in the described step (3).
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